Cyanide (cyanide)
Also known as: CN · cyanide ion
Cyanide is the highly toxic CN ion from electroplating, mining and chemical industries. The inland surface water effluent limit is 0.2 mg/L; public sewers 2.0 mg/L.
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What is Cyanide?
Cyanide (the CN⁻ ion and its compounds) is one of the most acutely toxic substances in the effluent standards — it blocks cellular respiration and is lethal to aquatic life and humans at very low concentrations. Reflecting this, its effluent limit is extremely tight: 0.2 mg/L for inland surface water and 2.0 mg/L for public sewers. Cyanide is additionally dangerous because, in acidic conditions, cyanide solutions release hydrogen cyanide gas (HCN), which is rapidly fatal by inhalation.
Cyanide is used and released in electroplating and metal-finishing (cyanide-based plating baths), gold and silver extraction (cyanide leaching), case-hardening of steel, and certain chemical processes. The plating and precious-metal-recovery uses are the ones that intersect with recycling.
For recyclers, cyanide is most relevant to e-waste precious-metal recovery. Recovering gold, silver and palladium from circuit boards and connectors has historically used cyanide leaching, and informal e-waste operations using crude cyanide-based gold recovery are a serious cyanide-pollution and worker-poisoning hazard. Electroplating-related waste and any metal-finishing residues entering the recycling stream can also carry cyanide. Hexavalent chromium and cyanide together are the signature toxics of plating-related effluent.
The practical points are stark: cyanide demands destruction before discharge and strict handling. Cyanide effluent is treated by alkaline chlorination or other oxidative destruction that breaks the cyanide down before it can be discharged or mixed with acidic streams (mixing cyanide and acid releases lethal HCN gas — a critical never-do). For e-waste recyclers, the strong recommendation is to avoid cyanide-based precious-metal recovery in favour of safer hydrometallurgical routes, and never to use informal cyanide gold-recovery methods, which cause both fatal poisonings and severe environmental contamination. Where cyanide is unavoidable, dedicated destruction treatment and rigorous segregation from acidic streams are mandatory.
Common questions about Cyanide
Plain-English answers to what people most often ask.
What is the cyanide limit in effluent in India?
Why is cyanide a risk in e-waste recycling?
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